A laser is a light-amplifying device capable of inducing high intensity coherent monochromatic light concentrated in a well-collimated beam, commonly referred to as a laser beam. A typical laser comprises an optical resonator having a laser-active material, i.e., a laser medium, that can be in the form of a solid, liquid or gas. When the laser medium is a liquid, it typically is in the form of a laser dye solution which comprises a laser dye dissolved in a solvent or a combination of solvents. In operation of a laser, the laser medium's atoms or molecules are pumped with sufficient energy to exceed a threshold energy value such that laser action is induced. Such photons trigger other molecules to emit similar photons prematurely, and together they form the laser beam.
Even though lasers have a wide variety of uses in such diverse areas as drilling, spectroscopy, welding, cutting, communication, analysis, surgery, and photochemistry, they normally can function only in a small portion of the light spectrum since they are dependent upon the laser media because the wavelengths emitted by a specific energy transition in a given laser medium is tunable over only a very limited portion of the light spectrum. It is therefore necessary to provide a number of different laser media in order to enable lasers to operate over the entire light spectrum. Further, many of the laser media available up to now have been solids or gases. But, traditionally it has been recognized that laser dye solutions can provide advantages not possible with gas or solid laser media. For example, there are several laser dye solutions known that are tunable over a relatively broad range of wavelengths. Also, the laser output from laser dye solutions can be tuned to a specific wavelength selected from a range of wavelengths. Tunability is a clear advantage over gaseous or solid laser media which typically emit at a single wavelength. Further, a single laser dye instrument can emit laser beams at a wide range of different wavelengths from the ultraviolet to the near infrared simply by changing to another laser dye liquid.
Laser dye solutions, however, are not without their shortcomings and disadvantages. One significant problem, for example, is the limited number of solvents or solvent combinations available for commercial use with jet stream dye lasers. This drawback unfortunately limits the selection of laser dyes for jet stream dye lasers to those which dissolve in the few solvents that are available in order to form effective laser dye solutions.
In the case where a laser dye solution is employed with a jet laser system, the laser dye solution is pumped through a nozzle with sufficient pressure to create a ribbon of dye solution upon which the pump source beam impinges. The use of a jet stream dye laser offers the advantage of a high output over a wide tuning range being pumped by, for example, argon-ion, krypton-ion, and Nd:YAG lasers as well as others. The use of jet stream dye lasers to produce dye jets, i.e., streams of carrier solvents containing dyes, requires utilization of viscous solvents. Viscous solvents provide for damping of surface waves produced by pressure fluctuations, irregularities in the nozzles and high laminar flow velocities which damping enhances the system's efficiency. One prior art solvent generally accepted for use in a jet stream laser is ethylene glycol (viscosity of approximately 20 centipoises at about 20.degree. C.) which typically is utilized by itself, or in combination with other solvents, in order to dissolve various laser dyes.
When utilizing an argon-ion or krypton-ion pumped jet stream dye laser, there are only a limited number, e.g., approximately fifteen or so, laser dyes available which have been generally accepted for use because ethylene glycol has been considered the base solvent of choice for the jet laser system. In other words, use of that solvent restricts the dye choice to those which have solubility either in ethylene glycol itself, or in a combination of solvents where one component is an additive that helps to solubilize the dye sufficiently so that it may be incorporated into the ethylene glycol. Of the laser dyes utilized today, however, it is believed only two are commercially used directly in ethylene glycol whereas the remainder require a combination of solvents to enhance their ease of dissolution. In the latter case, benzyl alcohol, propylene carbonate, dimethylsulfoxide, and methanol are examples of solubilizing enhancers employed to help solubilize the laser dyes in the ethylene glycol.
The solubilizing additives present further disadvantage of their own. For instance, the solubilizing additives are relatively low viscosity solvents typically requiring the addition of viscosity raising additives when used so their use in a jet stream laser may be limited. Furthermore, some of the solubilizing additives are somewhat hygroscopic which is detrimental due to the fact they tend to cause the solvent to take up water vapor from the atmosphere which reduces its viscosity and, therefore, its effectiveness in a jet stream laser. Still further, in some cases, such as with dimethylsulfoxide, the solubilizing agents are absorbed through skin presenting potentially hazardous health risks to personnel handling the laser dye solutions in which such solubilizing agents have been incorporated. And other solubilizing agents, such as propylene carbonate, tend to absorb the pumped light especially in the ultraviolet region which causes a loss in overall efficiency of the jet stream laser.
Consequently, it is the primary objective of this invention to provide new and improved commercially effective laser dye liquids comprising versatile solvents that are capable of dissolving a wide range of laser dyes without the need for solubilizing or viscosity altering additives, which do not interfere with the emission of coherent laser radiation when the laser dye liquids are pumped, and which are particular suited for use with jet stream lasers.